Vessels such as water kettles have been heating water for mankind for some time and the electric kettle has probably been the last link to evolve in the kettle chain of development. The first electric kettles were provided with a simple sheath covered electric heating element located in the bottom of the vessel which heated the water by heat transfer through the sheath into the water. A thermostat of the "reset" type was usually provided to protect the kettle against resulting damage during "boil dry."
Subsequently kettles evolved which could heat the water in the vessel at two substantially different rates. This was accomplished by providing two separately energizable elements in the bottom of the vessel so that by moving a switch either of the elements could be selected for energization. This kettle functioned to provide heated water in a very short time with vigorous boiling on the "fast boil" setting or if the kettle was set on the lower heat setting the kettle would evaporate the water in the vessel at a safe rate to perform the function of a vapourizer. The inclusion of a switch and a low heat element have functioned to add heat to the water in the vessel at two widely differing rates. Because of the inclusion of the two additional components required to give the "low heat" operation, substantial additional manufacturing costs were incurred during the manufacture of kettles of this type.